A primary by-product of commercial corn wet milling is wet corn gluten meal (CGM) which is typically concentrated and sold in dry form (approximately 90% solids). CGM is known to be most stable in dry form. Zein can be readily obtained by further processing of corn gluten meal. The potential yield of zein is about one pound per bushel of corn.
Corn gluten has been processed into varying grades of zein depending upon the particular end use, i.e., for use in plastics, protective coatings, inks, food products, pigments, adhesives and films, among other uses. In food applications, the quality of the zein is of paramount importance to the overall organoleptic properties of the food product. For instance, currently available grades of zein contain impurities that can impart off-flavors and colors (particularly yellow color--due to the presence of xanthophyll and carotene pigments) to the food product. Further processing of the zein to remove undesirable colors and off-flavors has been developed with limited success, particularly for use in foods.
Processes for producing "white" zein by extraction with ethylene dichloride (Mason and Palmer, J. Biol. Chem. 107:131-132 (1934)), benzene (U.S. Pat. No. 2,133,591 issued to Swallen) and other hydrocarbons (U.S. Pat. Nos. 2,287,649 and 2,272,488 both issued to Swallen; U.S. Pat. No. 2,229,870 issued to Pearce) have been described. Although the product has minimal color, the use of these solvents make the "white" zein unacceptable for use in the food and pharmaceutical industry.
Enzymatic modification of corn gluten by proteolytic hydrolysis to produce a flour-like material was previously described by Adler-Nissen (U.S. Pat. No. 4,100,151). Enzyme hydrolysis of crude gluten using alpha-amylase has also been described by Knight (U.S. Pat. No. 3,782,964). In both of these processes, the product generated is a modified gluten rather than zein.
Alcohol extraction of corn gluten to obtain zein has been described by Lawhorn (U.S. Pat. No. 4,624,805), Chen and Hoff (U.S. Pat. No. 4,716,218), Coleman (U.S. Pat. No. 2,355,056), Carter and Reck (U.S. Pat. No. 3,535,305) and Swallen (U.S. Pat. Nos. 2,287,649, 2,332,356, 2,105,760, 2,120,946, 2,133,591 and 2,272,488). In each instance, zein is extracted using a solvent (e.g., ethanol, isopropanol) and concentration for which zein is soluble therein. The extracted zein produced by these methods tend to contain impurities that are co-extracted and soluble in the extraction solvent. Further extraction of the impurities is necessary to adequately depigment and deflavor the zein product.
Thus, it is desirable to process corn gluten to generate a purified, food grade zein that is essentially decolored, deflavored and odor-free and suitable for use in food and pharmaceutical applications.